The present invention relates to a copier, facsimile transceiver, printer or similar image forming apparatus and, more particularly, to a sheet feed device incorporated in such an apparatus for automatically removing a wrapping from a sheet pack and then feeding unwrapped sheets one by one.
It has been customary with a conventional image forming apparatus to supplement sheets entirely by hand. Specifically, to supplement sheets, the operator pulls out a cassette or tray from the sheet feed device, removes the top cover of the cassette, unwraps a sheet pack, raises sheet pressing members or corner pawls disposed in the cassette, neatly arranges unwrapped sheets in a stack, loads the cassette with the sheet stack, puts the sheet pressing members on the sheet stack, and then sets the cassette in the device. Such a procedure including a great number of steps is time- and labor-consuming, especially for users who use a great amount of sheets.
In the light of the above, a sheet feed device has been proposed which allows the operator to set a predetermined number of sheets in the form of a sheet pack directly in the body thereof and automatically unwraps the pack and then feeds sheets by mechanisms built therein. For example, Japanese Patent Laid-Open Publication No. 203534/1988 discloses a method and an apparatus which allows the operator to stack multiple sheet packs each accommodating a predetermined number of sheets one above another, moves one of the sheet packs forward while cutting opposite sides of the wrapping of the pack with a cutter, sucks the top and bottom of the cut wrapping to remove it, gripping unwrapped sheets to bring them to a transport table, and then moves the transport table to a sheet loading position. On the other hand, Japanese Patent Laid-Open Publication No. 97145/1985 teaches an implementation using sheets accommodated in a box formed of cardboard, resin or similar relatively hard wrapping material. In this case, the operator removes the portions of the box which will contact a pick-up roller, separator pawl and so forth and then puts the box in a sheet feed position in the image forming apparatus. Such an implementation allows the box to serve as a cassette.
However, unwrapping a sheet pack by a cutter as stated above is undesirable since the cutter is apt to cut the sheets together with the wrapping. This problem is critical when it comes to, among others, a copier or similar image forming apparatus. Moreover, the suction used to remove the wrapping increases the overall size of the device while aggravating noise. On the other hand, the above-stated scheme using the transport table has a problem that gripping and transporting an unwrapped sheet stack is likely to disturb the neat stack and, in the worst case, scatters around the sheets. Moreover, cardboard, resin or similar hard wrapping material constituting the box is disproportionately expensive since it is expected to accommodate only several hundred sheets. The box is formed with perforations to allow the end portion thereof to be removed by the user. The perforations expose the sheets in the box to the atmosphere and, when the sheets are stored over a long time, cause the sheets to absorb moisture, adversely influencing image formation to be effected. In addition, the box has to be partly protruded to the outside of the device to be removed with ease. This is contradictory to the increasing demand for space saving.